This invention relates to an aluminum alloy. In particular, this invention relates to a dispersion strengthened aluminum alloy.
Aluminum alloys have been widely used in applications such as aircraft because of their relatively low cost, ease of fabrication and attractive mechanical properties. Various efforts have been made to further improve the strength of aluminum alloys, including the use of aluminum powder-derived alloy products wherein aluminum powder is produced, compacted and shaped into a useful article.
Conventional aluminum alloys lose their strength above about 150.degree. C. because strengthening precipitates coarsen rapidly and lose coherency. Powder metallurgy offers a means of dispersing intermetallic phases that resist coarsening, and provide significant strength up to about 350.degree. C. The approach generally is to add alloying additions, such as the transition metals or rare earth metals, with low solubility and low diffusion rates. Additionally, oxide, carbide, and intermetallic dispersion strengthening introduced by mechanical attrition provide strength at elevated temperatures and excellent room temperature strength after prolonged elevated temperature exposure.
Alloys developed by mechanical attrition have shown attractive stress-rupture properties, as well as excellent elevated-temperature stability. However, strength in the 230.degree.-345.degree. C. range has not been as high as that obtained by rapid solidifcation.
Rapidly solidified material is produced by rapidly quenching molten aluminum alloys which results in a fine dispersion of intermetallic particles for strengthening compacts formed by squeezing or compacting such aluminum powders, ribbons or particulates.
In general, there are two types of aluminum alloys strengthened with second phase particles. In heat treatable alloys, fine intermetallic particles, referred to as precipitates result in products with high strength and toughness. These are produced by solid-state heat treatment involving solutionizing the second phase particles, followed by quenching and aging steps to provide the desired fine distribution of second phase precipitates. On the other hand, non-heat treatable dispersion strengthened aluminum alloys rely on the production of fine incoherent intermetallics to strengthen the aluminum matrix by impeding dislocation motion (plastic flow) due to their close spacing. In this case, the second phase particles have little or no solubility in the solid state even at high temperatures. Thus, once produced, they are very thermally stable. They cannot be refined by solid state processing; they can only be refined by returning to the liquid state followed by rapid solidification. In this alloy class, it is extremely critical to carefully select alloy composition so a fine, thermally stable dispersoid is produced, since once a coarse distribution occurs, there is no solid-state heat treatment to refine the distribution as in the case of precipitation hardened systems. In both alloy types it is desirable to maintain the dispersoid and intermetallic particles in a fine size and spacing to achieve good combination of strength and toughness. Various alloy refinements and process refinements have gone forward in order to further the property gain achieved in the dispersion hardened alloys and there is a continuing desire to further improve the strength of compacted aluminum products produced therefrom.
U.S. Pat. No. 4,464,199 to Hildeman and Sanders, discloses aluminum-iron-rare earth metal alloys which exhibit significant improvement in yield strength over ingot material such as 2219--T852. Another promising inroad involves aluminum-titanium-rare earth metal alloys and the present invention concerns these alloys.
It is an object of the present invention to provide a novel aluminum alloy.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art.